Right so this is something I've been thinking about for ages and nobody really talks about it. I do a lot of EVP work near ley lines and I've noticed the same thing with other phenomena - high voltage corridors seem to act almost like a spine for weird activity generally.
My theory, and its probably not original, is that the electromagnetic fields along those corridors could be doing something to local perception or even attracting certain types of entity. Whether bigfoot is a flesh and blood creature or something stranger, EM sensitivity might be part of the picture.
The other angle is purely practical - power line corridors create these long strips of cleared land through woodland and bigfoot would absolutely use those as travel routes if it existed as a physical animal. So you might just be seeing movement corridors.
Probably both things are true to some degree. Has anyone actually mapped this out properly with GPS coordinates or is it still all anecdotal? Would be worth doing a proper overlay with reported sighting data.